linux-kernel - Re: GIT bisection range errors

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Message-ID: <20080509211017.GA15926@deepthought>
Date:	Fri, 9 May 2008 22:10:17 +0100
From:	Ken Moffat <zarniwhoop@...world.com>
To:	Roland Dreier <rdreier@...co.com>
Cc:	Rene Herman <rene.herman@...access.nl>,
	Adrian Bunk <bunk@...nel.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: GIT bisection range errors

On Thu, May 08, 2008 at 04:33:04PM -0700, Roland Dreier wrote:
>  > > $ git checkout -b rc v2.6.26-rc1
>  > > $ git bisect start
>  > > $ git bisect bad
>  > > $ git bisect good v2.6.25
>  > >
>  > > Yet, during this I'm finding myself at 2.6.25-rc6 and 2.6.25-rc8
>  > > as the last two results (both good...).
> 
>  >  I reported a similar thing at the beginning of April
>  > http://lkml.org/lkml/2008/4/2/390 - 2.6.25-rc1 bad, 2.6.24 good, git
>  > dropped me back at 2.6.24-rc4 (again, according to the top level
>  > Makefile).
> 
> This is normal and expected, due to the distributed nature of git and
> the fact that git-bisect operates on the full topology of history and
> not just a linear sequence of commits.
> 
> Imagine history like:
> 
>     A---B---C---D
>      \         /
>       \       /
>        \     /
>         E---F
> 
> where B is good and D is bad.  Now, when you bisect, there is no way to
> know whether, say, E is good or bad and hence the bisect process may
> present E as a tree to try.
> 
> Now, if B is the 2.6.25 release, then since E branched off before B, it
> will have a Makefile that says 2.6.25-rcX.  Which is exactly the
> behavior you are seeing.
> 
> In short, everything looks fine and is behaving as expected.
> 
>  - R.

 But, surely those of us who bisect against linus' tree only
care about the commits which made it into his tree, and in the
context of whatever else was in _his_ tree at the time ?

 Maybe I'm under a misapprehension about changesets and merges.  I
thought a merge was just pulling in a series of changesets, and that
each changeset only contains related items (comment, changed lines,
added files, deleted files).

 Whatever else may be in tree E, I don't expect it to have a commit
which changes $EXTRAVERSION, purely because tree E is not Linus'
tree.  To me, that field is somewhat special - it indicates where I am
(e.g. if bisecting across multiple rcs, or even across multiple
releases) and it determines where the modules will go.

 I see from Linus' reply to the original mail that this is indeed
normal.  That certainly isn't the word I would choose to use : we
give things names to describe them and in this case the EXTRAVERSION
appears to inhabit a parrallel universe to the pre-existing usage
of "2.6.24 good, 2.6.25-rc1 bad".   Colour me more confused than ever.

Ken
-- 
das eine Mal als Tragödie, das andere Mal als Farce
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